What % sodium chlorite is needed to produce mms

I remember reading a while back 4 years ago that an 85% sodium chlorite flakes are needed to produce the mms and that these flakes where not to be bought through chinese companies because of heavy metal contamination. But now powder is the norm because of the purity. So is buying the flakes through chinese companies still not the way to go.

So what do you buy and from where.
Powder over flakes.
US and canadian companies over chinese
80% now instead of 85%

Any help would be very much appreciated thanks